Incidentally, its on the pavement (2,3,3)
I believe the answer is:
by the way
'incidentally' is the definition.
(I know that incidentally can be written as by the way)
I don't understand the rest of the clue.
Can you help me to learn more?
(Other definitions for by the way that I've seen before include "In point of fact" , "At the roadside - incidentally" , "Incidentally, as a rather irrelevant comment" , "At the side of the path?" , "In passing, while we're on the subject" .)